dennison



May 10, 1955 E. s. DENNISON TWO STAGE HEAT PUMP SYSTEM 2 Shets-Sheet 1 Filed May 27, 1952 IN V EN TOR. [D0930 .S. PENN/$0M y 1955 E. s. DENNISON 2,707,869

TWO STAGE HEAT PUMP SYSTEM Filed May 27, 1952 K 2 Sheets-Sheet 2 48 1 l l I Q 23 y 8' T i l IN VEN TOR.

0 0 920 6. Davy sou 5 the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A two stage space heating system comprising a thermal reservoir, material of great heat storage capacity therein, a closed low temperature circuit containing a volatile working fluid and having a heat absorbing portion exposed to a relatively low temperature outside of said space and reservoir and having a heat radiating portion inside the reservoir, a low temperature compressor in said circuit for compressing the fluid therein after it has been vaporized in said heat absorbing portion to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in said circuit for expanding the condensed fluid therein to lower its temperature after it has given up heat to said material in the reservoir, a closed high temperature circuit containing a volatile working fluid and having a heat absorbing portion inside the reservoir and having a heat radiating portion outside of the reservoir, a high temperature compressor in the high temperature circuit for compressing the fluid therein after it has been vaporized in the reservoir to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in the high temperature circuit for expanding the condensed fluid therein to lower its temperature after it has dis charged heat from the radiating portion of the circuit, a thermostat responsive to said low temperature for stopping the operation of the low temperature compressor if said low temperature drops below a predetermined minimum, and a thermostat responsive to the temperature in said reservoir for by-passing the first-mentioned thermostat and starting the low temperature compressor operating when the temperature in the reservoir falls below a predetermined point while said low temperature is below said predetermined minimum.

2. A two stage space heating system comprising a thermal reservoir, material of great heat storage capacity therein, a closed low temperature circuit containing a volatile working fluid and having a heat absorbing portion exposed to a relatively low temperature outside of said space and reservoir and having a heat radiating portion inside the reservoir, a low temperature compressor in said circuit for compressing the fluid therein after it has been vaporized in said heat absorbing portion to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in said circuit for expanding the condensed fluid therein to lower its temperature after it has given up heat to said material in the reservoir, a closed high temperature circuit containing a volatile working fluid and having a heat absorbing portion inside the reservoir and having a heat radiating portion outside of the reservoir, a high temperature compressor in the high temperature circuit for compressing the fluid therein after it has been vaporized in the reservoir to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in the high temperature circuit for expanding the condensed fluid therein to lower its temperature after it has discharged heat from the radiating portion of the circuit, a normally closed electric switch operatively connected with the low temperature compressor, means responsive to a predetermined condition for opening said switch to stop the operation of the low temperature compressor, a normally open switch shunting the normally closed switch, and a thermostat responsive to the temperature in said reservoir for closing said normally open switch if the temperature in the reservoir falls below a predetermined minimum, whereby to start the low temperature compressor operating again if the normally closed switch is open.

3. A two stage space heating system comprising a thermal reservoir, material of great heat storage capacity therein, a closed low temperature circuit containing a volatile working fluid and having a heat absorbing portion exposed to a relatively low temperature outside of said space and reservoir and having a heat radiating portion inside the reservoir, a low temperature compressor in said circuit for compressing the fluid therein after it has been vaporized in said heat absorbing portion to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in said circuit for expanding the condensed fluid therein to lower its temperature after it has given up heat to said material in the reservoir, a closed high temperature circuit containing a volatile working fluid and having a heat absorbing portion inside the reservoir and having a heat radiating portion outside of the reservoir, a high temperature compressor in the high temperature circuit for compressing the fluid therein after it has been vaporized in the reservoir to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in the high temperature circuit for expanding the condensed fluid therein to lower its temperature after it has discharged heat from the radiating portion of the circuit, an electric circuit for operating the low temperature compressor, a normally closed electric switch in said circuit, means responsive to said low temperature for opening said switch if said low temperature drops below a predetermined minimum, a normally open switch shunting the normally closed switch, and means responsive to the temperature in said reservoir for closing said normally open switch if the temperature in the reservoir falls below a predetermined point while said low temperature is below said predetermined minimum.

4. A two stage space heating system comprising a thermal reservoir, material of great heat storage capacity therein, a closed low temperature circuit containing a volatile working fluid and having a heat absorbing portion exposed to a relatively low temperature outside of said space and reservoir and having a heat radiating portion inside the reservoir, a low temperature compressor in said circuit for compressing the fluid therein after it has been vaporized in said heat absorbing portion to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in said circuit for expanding the condensed fluid therein to lower its temperature after it has given up heat to said material in the reservoir, a closed high temperature circuit containing a volatile working fluid and having a heat absorbing portion inside the reservoir and having a heat radiating portion outside of the reservoir, a high temperature compressor in the high temperature circuit for compressing the fluid therein after it has been vaporized in the reservoir to raise its temperature before it enters said heat radiating portion and is condensed, an expansion valve in the high temperature circuit for expanding the condensed fluid therein to lower its temperature after it has discharged heat from the radiating portion of the circuit, an electric circuit for operating the low temperature compressor, two normally closed electric switches in series in said circuit, a thermostat responsive to said low temperature for opening one of the switches if said low temperature drops below a predetermined minimum, a clock for opening the other switch at predetermined times, a normally open switch shunting both of said normally closed switches, and a thermostat responsive to the temperature in said reservoir for closing said normally open switch if the temperature in the reservoir falls below a predetermined point while either of said normally closed switches is open.

References Cited in the file of this patent UNITED STATES PATENTS 1,808,494 Carney et al. June 2, 1931 2,241,070 McLenegan May 6, 1941 2,338,691 Tucker Ian. 4, 1944 2,453,823 Williams Nov. 16, 1948 2,497,450 Gygax Feb. 14, 1950 2,529,154 Hammond et al Nov. 7, 1950 2,637,983 Malkoif et al. May 12, 1953 Unite States Patent 1 2,707,869 TWO STAGE HEAT PUMP SYSTEM Edward S. Dennison, Jeannette, Pa. Application May 27, 1952, Serial No. 290,270 4 Claims. (Cl. 62-4) This invention relates to space heating systems, and more particularly to those using heat pumps.

In the past, heat pump systems have been employed in which a working fluid in a closed circuit is vaporized by heat from the ground or the ambient atmosphere, and then is compressed to raise its temperature to well over 100 F. so that it can be used for heating a room or the like. As the compressed fluid radiates heat, it condenses and then it is expanded to a lower pressure and temperature and recirculated through the system. Of course, power is required to drive the vapor compressor, but under normal operating conditions the quantity of heat made available for space heating is several times the heat equivalent of the power input. quantities is known as the coeflicient of performance. Its value normally is in the range of 3 to 4, but it may be reduced drastically if the ambient temperature is exceptionally low and the discharge temperature is re quired to be unusually high; that is, under severe winter conditions. Under such conditions economy of the system not only is very low, but the capacity of the heat pump suffers a serious drop due to the low density of compressor suction gas at reduced vapor pressure. These two effects combine to make the application of heat pumps, in their simplest form, unsatisfactory where a fairly low ambient temperature, for example F, may be encountered even for brief periods. The plant must be designed to meet the worst condition, and then it is oversize during most of its service life.

' The use of pipes buried in the ground as the ambient heat source, or the drilling of a well deep enough to meet the prevailing water table, help in avoiding extremely low atmospheric temperatures. Nevertheless, the installation cost is great, the equipment cannot be completed and shipped from the factory in working order, eiiectiveness of the heat source falls oif in continued use because of the formation of ice around the sub-surface coils, and a lowering of the water table may render a well-type installation useless.

An improvement on such a system has been proposed, in which the heat pump charges a thermal reservoir with heat that can be withdrawn to meet peak demands. It is intended that at normal winter temperatures the heat pump will deliver the full required supply of heat continuously, but during any short period of excessively low temperature the heat stored in the reservoir Will be drawn upon to supplement the reduced capacity of the pump at such times. Although such a plant offers definite gains over one without a thermal reservoir, a number of serious defects are apparent. Heat must be stored at a temperature higher than the maximum needed to meet radiation requirements in severe weather. This means that the heat pump must be operated under conditions of poor economy. Since heat is stored considerably above room temperature, thorough insulation is necessary, but continuous loss of heat will occur in spite of it. As the heat stored in the reservoir is used up, there is a continual decline of the temperature at which the heat is available. Although it is helpful to utilize a chemical phase change in the heat storing material in the reservoir to increase its capacity, this increase is usually distributed over a wide range, for example to F., rather than being confined to a narrow temperature zone. Finally, the compressor has to operate over the full range between ambient and reservoir temperatures.

It is among the objects of this invention to provide a space heating system utilizing the heat pump principle in The ratio of these two 2,797,869 Patented May 10, 1955 which heat is delivered to a reservoir at a minimum cost, in which the reservoir stores heat at or slightly above room temperature, in which a chemical phase change can be utilized advantageously in the heat storage material, in which the temperature at which heat is supplied to the space being heated can be maintained substantially constant,'in which heat pumps are used that are relatively small and have high coeflicients of performance, and which can be made in a compact unit that can be shipped and installed easily.

In accordance with this invention, a low temperature heat pump and a high temperature heat pump have a portion inside an intermediate temperature thermal reservoir in heat transfer relation with a material of great heat storage capacity. For best results, the material should be one that undergoes a chemical phase change in absorbing and giving up heat. The low temperature heat pump has its heat absorbing portion outside the reservoir exposed to a relatively low temperature, such as the ambient atmosphere. Whenever the reservoir is sufliciently charged with heat the operation of the low temperature heat pump compressor is stopped. The high temperature pump has its heat radiating portion outside the reservoir for heating, directly or indirectly, the space or area that is to be heated. Means is provided which is responsive to a predetermined condition, such as low ambient temperature or the time of day, for stopping the operation of the low temperature heat pump compressor. Means also is provided which is responsive to the temperature in the thermal reservoir for starting the operation of that compressor in case the reservoir temperature begins to fall too low.

The invention is illustrated schematically in the drawings, Fig. 1 showing an entire system, and Fig. 2 is a line drawing showing a modification.

It will be seen from Fig. 1 of the drawings that my space heating system is a two stage system including two heat pumps connected in heat exchange relation by a thermal reservoir. One of these is called a low temperature heat pump because the temperature limits between which it operates are normally lower than those of the other heat pump, which is called the high temperature heat pump. The low temperature heat pump is a closed circuit or cycle formed from piping 1 that contains a suitable volatile working fluid or refrigerant, such as Freon. The piping has a heat absorbing portion in any suitable conventional form, such as a coil or grid 2. This grid is exposed to a source of heat which will be at a relaitvely low temperature, such as the outside air during a cold period of the year, although it could be buried in the ground or laid in a pond or other body of water. At the outlet end of the grid there is a compressor 3 which is driven by an electric motor 4 connected in an electric circuit 5. As is well known, the Working fluid in the circuit is vaporized in the grid by the ambient heat and then is compressed by the compressor to raise its tem perature, preferably to between and F. This higher temperature vapor flows into the heat radiating portion 7 of the circuit located inside a thermal reservolr 3, where it may take the form of a coil or grid or the like. The reservoir is a sealed receptacle or tank filled with a material 9 that should have great heat storage capacity so that it will absorb much of the heat in the working fluid flowing through the grid. Of course, the reservoir may be insulated to reduce heat loss as much as possible. As the working fluid gives up heat in the reservoir it condenses to a liquid that flows into a small tank 11 containing a float controlled throttle valve 12. The liquid leaving the tank through this valve is expanded by it to a lower pressure and to a temperature lower than the ambient atmosphere so that it will be able to absorb heat again and become vaporized as it flows through the heat absorbing grid. When the reservoir is fully charged with heat, compressor motor 4 is stopped 

